over the period 1990 through 1994. In South America, the deforestation rate in the 1980s was about 750,000 ha/year. It is not known whether or not this rate has declined over the last years. In Brazil, about 70% of the deforested areas is converted into ranch land.
Much of the deforested areas in Latin America went into ranching, after initially being cropped. In Central America, pasture areas have increased from 3.5 million to 9.5 million ha and cattle populations more than doubled. For example, in Central America, livestock have increased from 4.2 million head in 1950 to 9.6 million in 1992 (Kaimonitz, 1995). In Asia and sub-Saharan Africa, the decline in the forest area is mainly the result of crop expansion.
In the temperate zones, extensive grazing livestock are usually produced with some harvested forage during the wintertime. Livestock produced in extensive grazing systems interact most closely with biodiversity in the form of wildlife. In both Australia and the U.S. these systems were heavily used in the late 19th century, and as a result degradation of the resource base occurred. Heavy use during the last century led to legislation controlling the use of the grazing resource and consequently has promoted rangeland health and improved range condition. Key issues driving how people utilize temperate ranges include fuel prices and privatization (Central Asia), heavy levels of fertilization (Europe), and concern over riparian areas (western U.S.).
In mixed farming systems, crops and livestock are produced on the same resource base. Globally this system produces the largest share of meat (54%) and milk (90%). Throughout the developing world, mixed farming is the main agricultural production system for smallholders. Developmentally, mixed farming systems provide farmers with an opportunity to reduce financial risk and smooth out production cycles. Farmers are able to take the highs and lows out of their production cycles because they have the capacity to provide livestock with higher-quality forages during winter or dry months of the year. In return, the sale of livestock products helps finance inputs for the farming enterprise; in addition, livestock provide traction for soil preparation. The mixed farming system is also a partially closed system where the manure can be utilized on the farm to build soil fertility while the milk and meat produced in the system flow out to urban markets. In many respects mixed farming systems have the capacity to promote healthy ecosystems and provide for economic development of the farmer, but, due to human population pressure, poverty, and poor infrastructure, these systems can negatively impact biodiversity and the environment at large.
Mixed farming systems tend to be transitional as livestock production shifts from an extensive grazing system to an intensively managed industrial system. McIntire et al. (1992) have documented the role population pressure has in integrating crop and animal agriculture and in promoting the integration of crop-livestock systems. They also discuss how further increases in population pressure drive farmers to become more specialized, therefore, causing the decomposition of the mixed farming system into more-intensive crop or livestock enterprises. Disaggregating livestock and crop agriculture may result in lower levels of biodiversity, for by keeping the two activities biodiversity can be promoted and may prevent the agricultural system from becoming too brittle (Holling, 1995).
Globally mixed farm types and the way livestock are used are extremely diverse. In Southeast Asia, for example, livestock and crop production is very intensive. Cattle are used for draft purposes and in turn consume high proportions of crop aftermath. In contrast, many mixed farming systems in temperate Organization for Economic Cooperation and Development (OECD) countries had and have the potential for being balanced systems. These types of farms have the capacity to produce various crops (e.g., maize) in a rotation with alfalfa, which in turn provides a forage resource for ruminant livestock and helps to replenish soil nutrients extracted in the production of cereal grains. Mixed farming and biodiversity interact at several crucial levels. First is the interaction with wildlife which can be positive or negative. Second, by replenishing soil fertility through manure application, the mixed farm can help provide a viable environment for soil microflora and microfauna. In developed countries there has been a tendency for farmers to focus on monoculture crop production. From a plant and animal perspective this makes these systems more brittle and exposed to major stresses. By maintaining livestock in these farming systems there is an opportunity to keep these systems more robust and encourage more fully the presence of various plants and animals.
Mixed farming systems can be broadly classified into those found in developed and developing countries. Developing country mixed farming systems contain several environmental issues which impact biodiversity. Soil erosion impacts both the people and plant/animal biodiversity in the various mixed systems. Pimental et al. (1995) estimated erosion rates of 30 to 40 ton/ha/year in some Asian, African, and South American systems. Bojos and Casells (1995) determined that in Ethiopia soil loses were 5 ton/ha/year in grazing lands used by crop-livestock farmers while erosion rates on crop lands were 42 ton/ha/year. Here livestock may be critical in maintaining soil fertility and soil organic matter levels. In Southeastern Asia adding pig and ruminant manure together may contribute up to 35% of the soil organic matter requirements, therefore providing an important source of organic matter. This is a crucial contribution because it is the only avenue available for farmers to improve soil organic matter (de Haan et al., 1997).
In developed countries, soil erosion and soil fertility are issues that impact biodiversity. In temperate zones soil losses of up to 15 ton/ha/year have been reported by Pimental et al. (1995). Soil fertility is impacted more by overfertilization than a lack of soil nutrients. Once soils become saturated with excess levels of nitrogen or phosphorus, these nutrients leach into above- and belowground water systems. Driving much of this overfertilization is the ease of importing feed and inorganic fertilizer. By importing these products into the mixed farming system, there becomes less of a need to balance animal feed and cropping activities through rotation and fallow systems.
The industrial system can be the most capital intensive of the livestock production systems. In general, it is a large concentration of livestock (particularly poultry and swine), but can also include small-scale periurban production in developing countries. Industrial systems do not produce their own feed; rather it is imported into the system from other locations within a country or, in some extreme cases, it is imported from other regions of the world. Industrial systems can impact biodiversity locally through the wastes they generate or off-site, where the feed is grown for use in the industrial system.
The industrial system has a threefold effect on biodiversity through:
• Waste production and its effects on terrestrial and aquatic ecosystems. These effects are often geographically confined to areas of high livestock densities. Eutrophica-tion and destruction of habitats is a common phenomenon in parts of northeastern Europe and the U.S. as well as in the densely populated areas of the developing world, in particular Asia and, to a lesser extent, Latin America. Ammonia emission leads to acidification of the environment and negatively affects ecosystem functioning and biodiversity.
• Demand for concentrate feed and resulting changes in land use and cropping intensity. The production of feed grains, in particular, adds additional stress on biodiversity through habitat loss and damages in ecosystem functioning.
• The requirement for extremely uniform animals of similar genetic composition contributes to within-breed erosion of domestic animal diversity.
But the industrial system has many advantages. First, the rapid development of industrial pig and poultry systems helps reduce total feed requirements of the total livestock sector to meet a given demand. Therefore, it may help to alleviate pressures leading to deforestation and degradation of rangelands, such as is happening in parts of Latin America and Asia, thus saving land and preserving biodiversity. Second, the feed-saving technologies developed for this system do not have scale effects and can be successfully transferred to mixed farming systems. The same holds true for animal waste prevention and treatment technologies that have been developed following regulations applied mainly to the industrial system. Therefore, the demand-driven industrial system generates a series of innovations that have spillover effects on the sector as a whole.
LIVESTOCK SYSTEM INTERACTION WITH BIODIVERSITY The Plant Community
Native plant communities naturally go through a series of successional changes, from low to high to low plant diversities while in the process of obtaining a state of climax (Clements, 1905). Grazing by livestock overlies this natural process. That is, grazing intensity interacts with and can modify the rate at which plant communities move toward climax. In addition, there is some evidence that indicates that for grazing to effect plant communities significantly requires a combination of grazing intensity and rainfall or fire events (Milchunas et al., 1988; Westoby et al., 1989).
An important concept in determining the status of plant community health is that of thresholds (Westoby et al., 1989). The threshold concept proposes that plant communities under grazing pressure do not deteriorate in a linear fashion. Rather, there is a series of levels which a plant community moves to when confronted with a series of pressures. Thresholds separate these levels. Within a level, plant communities can fluctuate in terms of biomass production and species composition, and recovery within a level is more easily accomplished (Archer et al., 1988). If grazing pressure is relaxed prior to a critical level or threshold, plant community recovery becomes less problematic.
Depending upon how livestock graze in a specific environment, biodiversity can increase or decrease. Either heavy or light grazing can lead to a reduction in biodiversity. Moderate grazing tends to promote patchiness of vegetation (CAST, 1996). Increased patchiness allows for diverse plant species to compete in a given environment. Therefore, by moderately grazing native rangelands, plant communities can be manipulated to maintain a desired level of plant diversity.
The semiarid and subhumid areas are some of the world's most important repositories of plant and animal biodiversity. For example, in Africa, Le Houerou (1991) estimates that rangelands contain about 3500 plant species, having a significant role in ruminant nutrition.
For the subhumid savannas, weed invasion is a major problem threatening biodiversity, and the role of livestock is only secondary. For example, the grass Imperata cylindrica in the Philippines and Indonesia now has infested more than 5 million ha. Invasion with broad-leafed plants and shrubs is more common in the savannas of Africa and the Americas.
There are a large number of cases that show that in well-balanced grazing systems, especially those using multispecies, plant biodiversity increases. An extensive review of grazing and production data of 236 sites worldwide, including many sites in the semiarid zone, showed no difference in biomass production, species composition, and root development in response to long-term grazing in the field (Milchunas and Lauenroth, 1993).
There are a variety of ways in which livestock can interact with wildlife communities. These include (Burkholder, 1952; Odum 1971; Mosley, 1994):
1. Neutralism, where neither species affects the other;
2. Direct interference or resource use competition, where both species inhibit each other;
3. Amensalism, where one species is inhibited and the other not affected;
4. Predation, where one species inhibits another by direct attack;
5. Commensalism, where one species is benefited by the presence of another but there is no impact on the second species;
6. Protocooperation, in which the interaction between species is favorable to both species but the association is not obligatory; and
7. Mutualism, the interaction is favorable to both species and the association is obligatory.
The extent to which the interaction between livestock and wildlife is neutral, negative, or positive is dependent upon how domestic livestock are managed in specific situations. Severson and Urness (1994) identify four ways livestock can be used to modify species that can, in turn, develop habitats that are favored by certain wildlife species. Such a modification is achieved by altering the composition of vegetation, increasing the productivity of selected species, increasing nutritive quality of forage, and increasing diversity of habitats by altering plant structure.
Riparian health is an important issue driving the monitoring and use of public grazing lands. However, it is often overlooked that any species of wildlife or livestock can overgraze these critical areas. A key example of such a situation exists today in Yellowstone National Park (YNP), the crown jewel of the U.S. national park system. It has recently been demonstrated that elk are severely overgrazing riparian areas in YNP. In a study comparing riparian areas in YNP and on the summer range of the U.S. Sheep Experiment Station (approximately 30 miles from YNP), it was shown that grazing of sheep had a more beneficial impact on riparian health, as measured by willow populations, a key indicator species (Figure 1). Furthermore, as a result of healthier willow communities on the Sheep Station, beaver populations are also in better condition. This work demonstrates that any grazing animal can cause environmental instability and/or degradation and that by using an appropriate livestock species environmental health can be maintained or increased (Kay and Walker, 1997).
Another key aspect which determines the type of wildlife-livestock interaction is diet preferences. Different types of wildlife and livestock prefer different plant types. For example, cattle select more grass in their diet than sheep which choose a combination of grass, forbs, and browse. The same type of diet selection patterns are evident in wildlife. Murray and Illius (1996) cite examples in the Serengeti of how small-bodied species, such as the Thompson's gazelle, are more selective
YNP Not Protected
Figure 1 Impact of elk and sheep grazing on willow communities: a measure of ecosystem health and herbivore grazing.
YNP Not Protected
Figure 1 Impact of elk and sheep grazing on willow communities: a measure of ecosystem health and herbivore grazing.
grazers than larger animals, such as topi and buffalo. By having diets which do not overlap helps maintain a broad diversity of plants. They further discuss the fact that grazing pressure in the Serengeti increases the overall spectrum of resource availability to animal communities. By cropping and trampling the tall grasses, larger ungulates increase the range and sward structures providing room for a greater variety of ungulate species.
The interaction between wildlife and livestock in ecosystems can be complex. First, there is increasing evidence of a grazing complementarity between wildlife and livestock. As shown by Schwartz and Ellis (1981), the dietary "overlap" between most wildlife species and livestock is rather limited. Mwangi and Zulberti (1985) and Western and Pearl (1989) showed that the combination of livestock raising and wildlife management resulted in an equal or better species wealth than any of these activities done individually. Furthermore, in national parks in Kenya such as Amboseli, where livestock is not permitted, biodiversity is decreasing, with an increase in unpalatable plant species and bush encroachment (W. K. Ottichilo, unpublilshed data). On the other hand, the same author points out that there are many degraded areas in Kenya due to combined wildlife-livestock pressure.
The driving forces leading to losses in animal biodiversity are habitat destruction, species introduction, and hunting (World Resources Institute, 1994). Habitat destruction is playing an important role in the developing world, especially in the subhumid savannas. In Africa, road construction and human immigration from the drier areas leads to habitat destruction of the vectors of African sleeping sickness. In turn, this lifts the protection of wildlife, which is tolerant to the disease. International agencies, including the World Bank, have also financed extensive vector clearance campaigns in West Africa. Traditionally, these campaigns used a combination of hand and aerial insecticide spraying, initially with organochlorines, to eradicate the tsetse fly. Nagel (1993) argues that pesticides from this period are still notable in some African birds.
Since the mid 1980s, compounds with shorter residual effect, such as synthetic pyrethroids, have been used. These second generation compounds caused substantial initial damage to the flora and fauna, but permanent effects were not observed with single spraying, for example, in the World Bank-funded tsetse clearance project on the Adamaoua Plateau of Cameroon (P. Muller, unpublished data). The permanent damage and high residue levels reported from this project came from repeated spraying in the border areas. Bush encroachment resulting from inappropriate grazing management was the most serious environmental damage. Land-use plans have often been advocated as the essential elements of tsetse clearance, and international financiers have made the preparation of such plans conditional to the financing of the eradication campaigns. However, the experience with the enforcement of such land-use plans has been dismal, as local authorities lacked the authority and means for their enforcement. A critical issue concerning these zones is that traditional land tenure practices have been even less robust in these more humid areas than in the drier areas. This lack of strong traditional tenure practices has been felt in sub-Saharan Africa after tsetse clearance operations, and as a result a rather anarchic settlement pattern developed.
In addition, hunting and culling of wildlife was encouraged in the past, because wildlife was thought to be a reservoir of diseases, such as rinderpest and malignant catarrhal fever, and carriers of disease, such as East Coast fever and trypanosomiasis (Grootenhuis et al., 1991), and competition for scarce grazing resources. However, the control of the above-mentioned diseases has improved considerably and there is a much better understanding of which particular species harbor specific diseases.
The costs and returns from wildlife, compared with livestock and agricultural production, are highly variable. At the level of the national economy, the opportunity cost of wildlife biodiversity conservation in protected areas, in terms of forgone livestock and agricultural production, seems to outweigh the income from tourism and forestry generated by these protected areas. For example, in Kenya, NortonGriffiths and Southey (1995) estimated the forgone livestock and agriculture from the parks at U.S.$ 203 million, while the revenue from these parks amounts to only U.S.$ 42 million. On the other hand, Engelbrecht and van der Walt (1993) estimated that the Kruger Park in South Africa contributed more than U.S.$ 110 million/year in tourism vs. a forgone production of only U.S.$ 6 million. At household levels, the comparative profitability of wildlife and livestock raising varies greatly, according to the ecological conditions and wildlife use (meat, trophy hunting, tourism). Overall, under present conditions of niche markets for game meat or tourism, wildlife ranching seems financially more attractive, though. For the communal areas, wildlife cannot provide the multiple functions of producing milk for subsistence and providing traction, fertilizer, and investment that livestock can. Without any doubt, the combination of wildlife and livestock is the most appropriate under those conditions.
A recent World Bank study gives comparative income levels from wildlife and livestock production on ranches for four African countries. In Ghana, investments in cattle had an economic rate of return (ERR) of close to zero, whereas private wildlife ranching had an ERR of about 8. In Kenya, financial return on investment (FRR) from game ranching was estimated at 7 to 12% vs. about 6 to 8% from livestock ranching. In Namibia, the study gave a wide range of net returns varying from 0 to 0.28 rands/ha under livestock, to 0.28 to 1.50 rands/ha under wildlife. In Zimbabwe, the FRR for livestock was about 2%, compared with 10% for wildlife. Economic returns per hectare were higher for ranching than for wildlife. All wildlife enterprises benefited from the special niche market, either through higher meat prices, or through revenue from tourism or trophy hunting (Bojos, 1996).
In fostering sustainable wildlife-livestock integration on communal areas, institutional constraints play a big role. Traditionally, there has been a rigid centralized and regulatory attitude of public institutions in the protection of wild animals. This was especially the case in East Africa, where wildlife management was typically organized by central administrations in a rather military fashion. There was no benefit sharing with the local population, whereas wildlife causes high financial cost to the local population because of crop damage and livestock loss due to predators and diseases. This has led to antagonistic reactions from many herding and farming communities. In addition, the interdiction, still in effect in many countries, of sport hunting and consumption precludes benefits from wildlife to be realized as an important part of the potential benefits (W. K. Ottichilo, unpublished data).
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